Multiple Telemetry and/or Charging Coil Configurations for an Implantable Medical Device System

ABSTRACT

Embodiments of an improved implantable medical device system for orientation-independent telemetry to and from the device are disclosed. The system includes an external controller which produces an electromagnetic field to induce a current in a coil in the implantable medical device and vise versa. In a preferred embodiment, the external controller comprises three orthogonal coils, each of which is potentially activated to generate or receive the electromagnetic field. Algorithms are disclosed to allow for the choice of one or more of the coils best suited for telemetry based on the chosen coil&#39;s orientation with respect to the telemetry coil in the implantable medical device. Because all three of the orthogonal coils are potentially activated if necessary, the result is that at least one of the coils will be in a proper orientation with respect to the coil in the implantable medical device, thereby improving telemetry efficiency. The disclosed techniques may be used to improve induction-based powering or charging of the device as well.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 11/622,395filed Jan. 11, 2007, to which priority is claimed and which isincorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to implantable medical devices,and more particularly, to a system for providing telemetry to animplantable medical device from an external controller.

BACKGROUND

Implantable stimulation devices are devices that generate and deliverelectrical stimuli to body nerves and tissues for the therapy of variousbiological disorders, such as pacemakers to treat cardiac arrhythmia,defibrillators to treat cardiac fibrillation, cochlear stimulators totreat deafness, retinal stimulators to treat blindness, musclestimulators to produce coordinated limb movement, spinal cordstimulators to treat chronic pain, cortical and deep brain stimulatorsto treat motor and psychological disorders, and other neural stimulatorsto treat urinary incontinence, sleep apnea, shoulder sublaxation, etc.The present invention may find applicability in all such applications,although the description that follows will generally focus on the use ofthe invention within a Spinal Cord Stimulation (SCS) system, such asthat disclosed in U.S. Pat. No. 6,516,227, which is incorporated hereinby reference in its entirety.

Spinal cord stimulation is a well-accepted clinical method for reducingpain in certain populations of patients. As shown in FIGS. 1A and 1B, aSCS system typically includes an Implantable Pulse Generator (IPG) 100,which includes a biocompatible case 30 formed of titanium for example.The case 30 typically holds the circuitry and power source or batterynecessary for the IPG to function, although IPGs can also be powered viaexternal RF energy and without a battery. The IPG 100 is coupled toelectrodes 106 via one or more electrode leads (two such leads 102 and104 are shown), such that the electrodes 106 form an electrode array110. The electrodes 106 are carried on a flexible body 108, which alsohouses the individual signal wires 112 and 114 coupled to eachelectrode. The signal wires 112 and 114 are connected to the IPG 100 byway of an interface 115, which may be any suitable device that allowsthe leads 102 and 104 (or a lead extension, not shown) to be removablyconnected to the IPG 100. Interface 115 may comprise, for example, anelectro-mechanical connector arrangement including lead connectors 38 aand 38 b configured to mate with corresponding connectors 119 a and 119b on the leads 102 and 104. In the illustrated embodiment, there areeight electrodes on lead 102, labeled E₁-E₈, and eight electrodes onlead 104, labeled E₉-E₁₆, although the number of leads and electrodes isapplication specific and therefore can vary.

As shown in FIG. 2, the IPG 100 typically includes an electronicsubstrate assembly 14 including a printed circuit board (PCB) 16, alongwith various electronic components 20, such as microprocessors,integrated circuits, and capacitors mounted to the PCB 16. Two coils aregenerally present in the IPG 100: a telemetry coil 13 used totransmit/receive data to/from an external controller 12 as explainedfurther below, and a charging coil 18 for charging or recharging theIPG's power source or battery 26 using an external charger (not shown).A feedthrough assembly 24 routes the various electrode signals from theelectronic substrate assembly 14 to the lead connectors 38 a, 38 b,which are in turn coupled to the leads 102 and 104 (see FIGS. 1A and1B). The IPG 100 further comprises a header connector 36, which amongother things houses the lead connectors 38 a, 38 b. The IPG 100 canfurther include a telemetry antenna or coil 13 (discussed further below)for receipt and transmission of data to an external device such as ahand-held or clinician programmer (not shown), which can be mountedwithin the header connector 36. As already mentioned, the IPG 100usually also includes a power source, and in particular a rechargeablebattery 26.

Further details concerning the structure and function of typical IPGsand IPG systems are disclosed in U.S. patent application Ser. No.11/305,898, filed Dec. 14, 2005, which is filed herewith via aninformation disclosure statement and which is incorporated herein byreference.

As one can appreciate, IPGs require programming data to function asrequired for a given patient. Typically, such programming data iswirelessly telemetered into the IPG 100 from the external controller 12.An exemplary external controller 12 is typically flat and fits in apatient's or clinician's hand for easy portable use in programming theIPG 100.

Wireless data telemetry between the IPG 100 and the external controller12 is typically based on magnetic induction, and so requires telemetrycoil 17 in the external controller 12 and telemetry coil 13 the IPG 100.When data is to be sent from the external controller 12 to the IPG 100,coil 17 is energized with alternating current (AC), which induces anelectromagnetic field, which in turn induces a current in the IPG'stelemetry coil 13. The power used to energize the coil 17 can come froma battery or batteries in the external controller (not shown), from awall outlet via a plug (not shown), etc. The induced current can then betransformed at the IPG 100 back into the telemetered data signals. Toimprove the magnetic flux density, and hence the efficiency of theenergy transfer, the IPG's telemetry coil 13 may be wrapped around aferrite core 13′. As is well known, inductive transmission of data fromcoil 17 to coil 13 can occur transcutaneously, i.e., through thepatient's tissue 25.

Optimally, IPG systems are simple enough that a patient or clinician canuse the external controller 12 without medical supervision. This usuallyrequires instruction on how to best use the external controller 12 inrelation to the implanted IPG 100. Because the external controller 12and IPG 100 are typically both flat, users are told that telemetry willbe most efficient and effective when the distance between the externalcontroller 12 and the IPG 100 is minimized; when the planes of these twodevices are parallel; and when the devices “overlap” one another throughthe patient's tissue 25. Such instruction results from an understandingof the electromagnetic interaction of the coils 17 and 13, which isshown in FIG. 3. Shown is the optimal orientation of the two coils 17,13 with respect to each other, with both coils lying in planes 50, 52parallel to each other, and with the axis of both coils 54, 56 beingcolinear. When such an ideal condition is met, and assuming the distanceD between the two coils is also minimized, energy transfer from coil 17in the external controller 12 to coil 13 in the IPG 100 will bemaximized.

However, realization of this ideal condition necessarily relies onsuccessful implementation by the user of the external controller 12. Forexample, and as shown in FIG. 4, if the angle θ between the axis 54 ofcoil 17 and the axis 56 of coil 13 is non-ideal (i.e., non-zero), energytransfer will be non-ideal, which means that data may not betelemetered. When the axes 54, 56, are perpendicular, theoretically noenergy will be transferred, and realistically only a negligible amountof energy will be transferred. Another non-ideal orientation betweencoil 17 and coil 13 is shown in FIG. 5. In this instance, the axes 54and 56 of the coils are parallel, as are their planes 50 and 52, butthey are not colinear, with the result that the coils are notoverlapping. This too adversely impacts energy transfer from coil 17 tocoil 13.

The non-ideal orientations depicted in FIGS. 4 and 5 illustrate that auser of an external controller 12 must be attentive to proper placementof the controller 12 relative to the IPG 100 and to the instructionsnoted earlier. Requiring correct implementation by the user is of coursea drawback of such traditional IPG system hardware, because it isunrealistic to assume that any given user will be so attentive, and as aresult data telemetry may be adversely affected.

Further exacerbating the potential problem of improper externalcontroller-to-IPG orientation is the recognition that such an improperorientation is not necessarily always the result of user inadvertence.It has so far been assumed that it is relatively easy for the user tounderstand or infer the positioning of the coils 17 and 13. For example,when both the external controller 12 and the IPG 100 are basically flat,placing the coils 17, 13 close to the ideal orientation depicted in FIG.3 is not difficult. But what if the external controller 12 or IPG 100 isnot flat? What if the coils are mounted inside the housings in a mannerin which the coil position cannot be inferred? What if the IPG 100 isimplanted deep within a patient, such that the orientation of its coil13 cannot be inferred through the patient's tissue? What if the IPG 100moves or rotates within the patient after it is implanted? Any of theseeffects can make it difficult or impossible for even an attentive userto properly align the coil 17 in the external controller 12 and the coil13 in the IPG 100.

An improved solution to this coil alignment problem would be one inwhich proper alignment between the external controller 12 and the IPG100 could be reasonably assured, independent of their relativeorientations. This disclosure provides embodiments of such a solution.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B show an implantable pulse generator (IPG), and themanner in which an electrode array is coupled to the IPG in accordancewith the prior art.

FIG. 2 shows a cross-sectional view of a prior art implantable pulsegenerator and an external controller.

FIG. 3 shows an ideal orientation between the telemetry coils in the IPGand the external controller to maximize energy transfer.

FIGS. 4 and 5 show non-ideal orientation between the telemetry coils inthe IPG and the external controller.

FIG. 6 shows an embodiment of the invention in which three orthogonaltelemetry coils are provided in the external controller.

FIG. 7 shows an embodiment of the external controller having threeorthogonal telemetry coils in which the coils are wound around orintegrated with various electronic components in the externalcontroller.

FIGS. 8 and 9 show examples of the circuitry used to simultaneouslystimulate the three orthogonal coils, where the figures respectivelyshow the coils in serial and parallel configurations.

FIGS. 10 and 11 show examples of the circuitry used to independentlystimulate the three orthogonal coils.

FIGS. 12A and 12B show algorithms useable with embodiments of theinvention for choosing one of the three orthogonal coils as the coil tobe used during telemetry.

FIG. 13 shows an alternative embodiment of the invention in which thethree orthogonal telemetry coils are provided in the IPG.

FIG. 14 shows an alternative embodiment of the invention in which threeorthogonal telemetry coils are used in both the external controller andthe IPG.

FIG. 15 shows an alternative embodiment of the invention in which onlytwo orthogonal coils are used in the external controller.

Corresponding reference characters indicate corresponding componentsthroughout the several views of the drawings.

DETAILED DESCRIPTION

The following description is of the best mode presently contemplated forcarrying out the invention. This description is not to be taken in alimiting sense, but is made merely for the purpose of describing thegeneral principles of the invention. The scope of the invention shouldbe determined with reference to the claims and their equivalents.

The description that follows relates to use of the invention within aspinal cord stimulation (SCS) system. However, it is to be understoodthat the invention is not so limited. Rather, the invention may be usedwith any type of implantable medical device system that could benefitfrom improved techniques for providing orientation independence betweenan external controller and the device. For example, the presentinvention may be used as part of a system employing an implantablesensor, an implantable pump, a pacemaker, a defibrillator, a cochlearstimulator, a retinal stimulator, a stimulator configured to producecoordinated limb movement, a cortical and deep brain stimulator, or inany other neural stimulator configured to treat any of a variety ofconditions.

Embodiments of an improved IPG system for orientation-independenttelemetry in an IPG are disclosed. As shown in FIG. 6, an embodiment ofthe solution proposed herein replaces the single coil 17 in the externalcontroller 12 (see FIG. 3-5) with three orthogonal telemetry coils 60a-c, each of which is potentially energized by the external controller12 as explained further below. Because all three of the coils 60 a-c arepotentially energized if necessary, the result is that at least one ofthe coils 60 a-c will be sufficiently parallel with the plane 52 of thetelemetry coil 13 in the IPG 100, to allow for suitable data telemetry.At a minimum, no orientation of the external controller 12 with respectto the IPG 100 will result in a condition in which an insignificantamount of electromagnetic energy 29 is transferred between thecontroller coils 60 a-c and the IPG's coil 13.

In FIG. 6, the three orthogonal coils 60 a-c are shown as wrapped arounda block 61. This block 61 can comprise a ferrite core, which, as notedearlier, increases the magnetic flux density to increase the energy 29transfer between the coils 60 a-c and the IPG coil 13. Alternatively,block 61 can comprise other structures or materials, or could representan air core. Furthermore, as shown in FIG. 7, the coils 60 a-c can bewound around or integrated with various electronic components in theexternal controller 12. Thus, as shown, the external controller 12comprises a printed circuit board 64, which can include the variouscircuitry such as a microcontroller, a transceiver and switchingcircuitry (to be discussed in further detail below), etc. Batteries 66are also shown, which provide power to the printed circuit board 64 andits associated circuitry. Also shown is a ferrite core 63, which as justnoted is helpful in increasing magnetic flux density. As shown, thethree telemetry coils 60 a-c are wound around these components invarious manners such that their axes are orthogonal, just as they areshown in FIG. 6. While FIG. 7 illustrates one way of winding the coils60 a-c around the various components in the external controller 12, suchcoils can be wound in any myriad of ways to the same beneficial end ofcreating an external controller which is largely orientation-independentwith respect to the IPG 100.

FIGS. 8 and 9 show examples of the circuitry in the external controller12 used to simultaneously stimulate the three orthogonal coils 60 a-c,and respectively show the coils in serial and parallel configurations.As is typical, the coils 60 a-c are coupled to transceiver (XCV)circuitry 65, which is controlled by a microcontroller 70. Because thecoils 60 a-c may be used to receive information communicated back fromthe IPG 100, transceiver (i.e., transmitter and receiver) circuitry 65is preferred. However, if the coils 60 a-c are used exclusively forproviding energy 29 to the receiving coil 13 in the IPG 100 without alsoreceiving any back telemetry from the IPG 100, then only transmittercircuitry 65 would be necessary in the external controller 12. Themicrocontroller 70, as well as controlling the transceiver circuitry 65,controls other aspects of the external controller 12, such as chargingof its batteries 66 (see FIG. 7), receiving and processing user inputssuch as various button presses (not shown), providing indications touser regarding the status of telemetry, etc.

Because the magnetic field emitted by the telemetry coils 60 a-c is AC(alternating current), the coils 60 a-c are made to resonate as an LCcircuit, as is well known. The capacitance necessary for such resonancecan be positioned in parallel with the coils, or in series with thecoils, both of which are shown in dotted lines in the figures. For thefield to resonate with an appropriate frequency or within an appropriatefrequency band, it is necessary to tune the inductance of the coilsand/or the capacitance(s), again, as is well known.

In the embodiments of FIGS. 8 and 9, all three coils 60 a-c areenergized simultaneously, with the effect that three generallyperpendicular fields are produced for receipt by the IPG's telemetrycoil 13. While suitable in some applications, it should be noted thatsimultaneously-stimulated coils may have drawbacks. For example, it maybe more difficult to simultaneously tune the resonance of the coils.Also, because each of the coils 60 a-c will produce a field, thoseorthogonal fields may interfere with one another such that nulls mightbe present at some points in the overall field produced. However, theseeffects can be minimized by simulation and modeling. Furthermore, theapproach of FIGS. 8 and 9 will necessarily require energizing all of thecoils 60 a-c, even if a given coil does not significantly contribute totelemetry, e.g., because the axis of that coil is perpendicular to theaxis 56 of the IPG coil 13 (see, e.g., FIG. 4).

Because of these concerns or potential inefficiencies, in the preferredimplementation of the invention, the orthogonal telemetry coils 60 a-care independently and individually energized, such as through use of thecircuitry of FIGS. 10 and 11. As seen in those circuits, a switch 75 isprovided for establishing control of a single of the coils 60 a-c at anygiven time. The switch 75 can either be placed between themicrocontroller 70 and the transceivers 65 a-c for each of the coils 60a-c (FIG. 10) or can be placed between a single transceiver 65 and thecoils 60 a-c (FIG. 11). Although it requires multiple transceivercircuits 65 a-c, the approach of FIG. 10 provides better flexibility, asit allows each coil 60/transceiver 65 pair to be individually tuned. Ineither version of the external controller circuitry, a switching signal76 from the microcontroller 70 indicates to the switch 75 which of thecoils 60 a-c is presently used.

Regardless of the embodiment used for the external controller circuitry(either FIG. 10 or 11), such circuitry can be used in many differentways to establish telemetry with a given IPG 100. For example, accordingto a very simple protocol, each of the telemetry coils can besequentially activated (60 a, then 60 b, then 60 c, then 60 a, etc.),with each coil 60 a-c sending the same portion of programming data. Asnoted before, because at least one of the coils 60 a-c would have anappropriate orientation vis-à-vis the IPG coil 13, satisfactorytelemetry would be accomplished. But such sequential coil activation,while simple to implement, is potentially wasteful of time, and of theexternal controller 12's power, because it is likely that at least oneof the coils 60 a-60 c is not making a significant contribution totelemetry.

Accordingly, the external controller circuitry of FIG. 10 or 11 ispreferably used in accordance with an algorithm that selects the mostideal of the coils 60 a-c as the one to be used during telemetry to theIPG. FIGS. 12A and 12B illustrate exemplary algorithms useful in thisregard. One skilled in the art will realize that these algorithms areeasily implemented using the microcontroller 70 in the externalcontroller 12. The algorithms as depicted in flow chart form areself-explanatory, and so are not belabored here.

Both algorithms rely on sending test signals from the externalcontroller 12 to the IPG 100 prior to beginning actual telemetry toassess the transmission efficiency of each of the telemetry coils 60a-c. These test signals are sent from one of the coils 60 a-c in theexternal controller 12. After sending the test signal, the externalcontroller 12 waits for an acknowledgment response from the IPG 100 andassesses the signal strength of that response using the particularsending coil as the receiving antenna. In that regard, the circuitry inthe external controller 12 contains one or more reception detectors (RD)69 (FIGS. 10 and 11) for assessing the signal strength of the receivedacknowledgment signal, which can occur in numerous places in thecircuitry, but which is most logically associated with the transceivercircuit(s) 65. Reception detection of this type is known in the art ofimplantable medical device systems, and thus such details are notdiscussed here.

The main difference between the two algorithms depicted in FIGS. 12A and12B is whether all coils 60 a-c are necessarily tested. In the algorithmof 12A, all coils 60 a, 60 b, and 60 c are sequentially used to send atest signal, and the signal strength of the acknowledgement response isassessed for each. The coil with the highest received signal strength(coil X) is provisionally chosen as the coil to be used duringtelemetry, although to ensure that this coil is acceptable, the signalstrength is compared against a pre-set threshold chosen to ensuresuitable transmission efficiency. If the signal strength of the receivedresponse at coil X exceeds the threshold, then coil X is thereafterchosen as the optimal coil for telemetry, and telemetry can thereaftercommence using coil X. If the signal strength of the received responseat coil X does not exceed the threshold, then the external controller 12indicates to the patient that the controller 12 is not properly located.Such indication can occur for example by lighting an appropriate LED onthe case of the external controller 12, or by providing a message intext or an icon on a display such as a LCD as is well known.

The algorithm of FIG. 12B is similar, but does not bother to check thetransmission efficiency of subsequent telemetry coils 60 a-c if asuitable coil has been determined. Thus, like the algorithm of FIG. 12A,the algorithm of FIG. 12B sends a test signal from a first coil (e.g.,60 a) and assesses the strength of the response back at coil 60 a. Ifthe response received at the first coil exceeds the threshold, then thefirst coil is thereafter chosen as the optimal, and telemetry canthereafter commence using the first coil. If the threshold is notexceeded, then the second coil (e.g., 60 b) is assessed, and if it isacceptable, it is chosen. Otherwise the third coil (e.g., 60 c) isassessed, etc., until such time as either the third coil is deemedacceptable as the telemetry coil of choice, or the user of the externalcontroller 12 is notified of the out-of-position condition as explainedabove. In short, the algorithm of FIG. 12B does not necessarily assesseach of the coils 60 a-c, but instead stops when a suitable coil isdetermined.

A preferred first step in each algorithm, and particularly in thealgorithm of FIG. 12B, is to establish a default coil which is assessedfirst. For example, consider an external controller 12 having a basicflat shape such as is shown in FIG. 6. Assuming the user attempts to usesuch an external controller 12 as expected, it would be expected thatcoil 60 a would have the most efficient orientation with respect to thecoil 13 in the IPG 100. Accordingly, it is sensible to check this coil60 a first, because if the algorithm of FIG. 12B is used, it will likelyresult that coil 60 a is chosen as acceptable, and time and energy willnot be spent to assess coils 60 b and 60 c. While 60 a might be thepreferred default coil, a secondary preferred coil (e.g., either 60 b or60 c) can be automatically assessed as the next in line.

The default coil to be used (or, more generally, the order in which thecoils will be assessed) can also be established based on historicalresults. For example, if history shows that transmission coil 60 b hasthe highest response signal strength 90% of the time, and that coil 60 chas the highest response signal strength 9% of the time, coil 60 b canbe used as the default, followed by coil 60 c, and coil 60 a. Suchhistory can be stored the in ancillary steps shown in dotted lines inFIG. 12B. As shown, when a particular coil is determined to be optimalfor telemetry, that fact is recorded in a memory 80 associated with themicrocontroller 70 (FIGS. 10 and 11). Thus, when the algorithm of FIG.12B starts, this past history in memory 80 can be queried to determinethe most logical order for assessment of the various coils 60 a-c.

In each of the algorithms illustrated in FIGS. 12A and 12B, only one ofthe telemetry coils 60 a-c is actually chosen as the coil to be usedduring telemetry. However, in other embodiments of the algorithm, morethan one of the coils 60 a-c might be chosen. For example, if coils 60 aand 60 c both exhibit suitable signal strength responses, each can bechosen as coils to be used during telemetry. In such a case, it would bepreferable to cyclically activate each independently: first coil 60 a,then coil 60 c, then coil 60 a again, etc. Or, both of the chosen coils60 a and 60 c, if properly tuned, could be stimulated at the same time.This would of course require a switch 75 (FIGS. 10-11) which, inconjunction with switching signal 76, allows simultaneous connectionsbetween the microcontroller 70 and a plurality of the coils 60 a-c. Sucha scheme would mean that any given block of data is telemetered twice:once from coil 60 a and once from 60 c. While such redundancy might betime and energy inefficient, such redundancy may also be useful inimproving the reliability of the data transfer and ease of use to theuser.

FIGS. 13-15 illustrate different but related ways of rendering theexternal controller 12 and IPG 100 orientation independent with respectto each other. For example, in FIG. 13, the coil 13 in the IPG 100 (seeFIGS. 3-5) is replaced with orthogonal device coils 62 a-c, while theexternal controller 12 retains its singular telemetry coil 17. From afield interaction standpoint, the configuration of FIG. 13 is not verydifferent from the configuration of FIG. 6 in which the telemetry coils60 a-c in the external controller 12 are made orthogonal. Because of theorthogonal orientation of the three coils 62 a-c in the IPG 100,stimulation of the external controller's coil 17 will induce anon-negligible current in at least one of the IPG's telemetry coils 62a-c. As is the case when the orthogonal coils are placed in the externalcontroller (FIG. 6), the circuitry useable when the orthogonal coils 62a-c are within the IPG can be similar to those illustrated in FIG. 8-11,a point which recognizes that the coils are essentially similar whetherthey act as transmitters (e.g., in the external controller 12) orreceivers (e.g., in the IPG 100).

Moreover, the algorithm for using the multiple orthogonal coils 62 a-cin the IPG 100 can mimic either of the approaches of FIGS. 12A and 12B,although additional consideration is given to the fact that it isgenerally preferred in implantable technology to not continuallyenergize the telemetry reception circuitry in the IPG 100, which mightbe wasteful of IPG power. Accordingly, the IPG 100 reception circuitry“wakes up” (i.e., is powered) only periodically (e.g., for 1 ms everysecond or so) to sense whether a significant amount of induced currenthas been received at one of the IPG's orthogonal telemetry coils 62 a-c.Starting with a logical default device coil 62 (as described earlier),the received signal strength is assessed. If a suitable signal strengthis received (i.e., above a given threshold), then that coil 62 can bechosen as the telemetry receiving coil, akin to the approach of FIG.12B. Alternatively, the received signal strength can be assessed for allof the device coils 62 a-c, with the coil with the highest signalstrength being chosen by switch 75 as the coil for receiving telemetry,akin to the approach of FIG. 12A.

The embodiment of FIG. 13, in which the orthogonal device coils 62 a-care provided in the IPG 100 as opposed to the external controller 12, iscertainly viable. However, it is preferred to use orthogonal coils inthe external controller 12 (FIG. 6), instead of in the IPG 100 (FIG.13). This is because space and power within the IPG 100 is typicallylimited, and the extra overhead of additional coils and additionalelectronics would generally militate that the orthogonal coils be placedin the external controller 12, where space and power consumption is lessof a concern.

FIGS. 14 and 15 illustrate still further embodiments. In FIG. 14, boththe external controller 12 and the IPG 100 contain three orthogonaltelemetry coils 60 a-c and 62 a-c. Such a configuration allows for thehighest signal strength combination of any of the coils 62 a-c and ofthe coils 60 a-c to be chosen for telemetry. Of course, this approachrequires additional circuitry and algorithmic complexity.

FIG. 15 illustrates an embodiment in which only two orthogonal telemetrycoils 60 a and 60 b are used. Such coils are shown in the externalcontroller 12, but could also appear in the IPG 100 as explainedearlier. In this embodiment, the provision of two orthogonal coils 60 aand 60 b increases the likelihood of an efficient orientation betweenthe external controller 12 and the IPG 100 when compared with the singlecoil approaches of the prior art (see FIGS. 3-5), but requires lesshardware and algorithmic complexity than when three orthogonal coils areused (FIGS. 6-13). Of course, using only two orthogonal coils 60 a, 60 balso reduces operational flexibility, because an orientation is possiblewhich will result in negligible coupling between either of the telemetrycoils 60 a and 60 b and IPG coil 13 (i.e., when the axis of the missingorthogonal coil is parallel to the axis of the IPG coil 13). Butregardless, the provision of two orthogonal coils provides a wider rangeof acceptable external controller-to-IPG orientation profiles whencompared with the single coil approach of the prior art.

While it is preferred that the multiple coils be orthogonal, it shouldbe recognized that it is not strictly necessary for the multiple coilsin either the external controller 12 (FIGS. 6-13) or the IPG 10 (FIG.13) be at right angles to one another. Indeed, orientation freedombetween the external controller 12 and the IPG 100 can be achieved evenwhen the axes of the coils are not at right angles, but instead are atacute or obtuse angles with respect to each other, i.e., when thetelemetry coils are wound around axes that are not parallel to eachother. Moreover, recognizing that the axes of the coils can be arrangedat angles other than 90-degrees, it should be apparent that more thanthree coils can be used. To cite one example exhibiting a naturalsymmetry, four telemetry coils could be arranged such that their axeshave a tetrahedral orientation. Of course, such symmetry is notrequired, and the axes of the multiple coils could have other randomangles with respect to each other.

It is preferred that the disclosed technique be used in the context oftelemetry, i.e., with respect to those coils in either the externalcontroller 12 or the IPG 100 that are involved in data transmissionbetween the external controller 12 or the IPG 100. However, it should benoted that the disclosed techniques can also be used to improveinduction between those coils involved in powering a RF powered IPG orin charging the battery 26 of a rechargeable IPG, 26 (see FIG. 2). Asnoted earlier, an IPG 100 typically contains a coil 18 (FIG. 2) forreceiving induced energy from an external source (not shown), which maybe integrated with the external controller 12 or may be another externaldevice wholly discrete from the external controller 12. Properorientation of the external device's coil with the coil 18 in the IPGcan also be of concern, and therefore the use of orthogonal coils ineither the external device or the IPG (but preferably in the externaldevice) can benefit this aspect of IPG systems.

Although particular embodiments of the present invention have been shownand described, it should be understood that the above discussion is notintended to limit the present invention to these embodiments. It will beobvious to those skilled in the art that various changes andmodifications may be made without departing from the spirit and scope ofthe present invention. Thus, the present invention is intended to coveralternatives, modifications, and equivalents that may fall within thespirit and scope of the present invention as defined by the claims.

1. An external device for communicating with or providing power to animplantable medical device, comprising: a plurality of coils each woundaround an axis, wherein none of the axes are parallel to each other;transceiver circuitry coupled to the plurality of coils; and controllercircuitry for controlling the transceiver circuitry by executing analgorithm, the algorithm comprising: transmitting a test signal from afirst of the plurality of coils; receiving at the first coil a responseto the test signal from the implantable medical device; assessing theresponse at the controller circuitry; repeating the above steps forsubsequent of the plurality of coils until all coils have been assessed;choosing at least one of the coils based on the assessed responses; andactivating the chosen at least one coil to telemeter data or power to bereceived by at least one device coil in the implantable medical device.2. The external device of claim 1, wherein the external device is sizedto fit a user's hand.
 3. The external device of claim 1, wherein thecontroller circuitry comprises a microcontroller.
 4. The external deviceof claim 1, wherein the plurality of coils are wound around axes thatare orthogonal to each other.
 5. The external device of claim 1, whereinonly one of the plurality of coils is chosen.
 6. The external device ofclaim 1, wherein assessing the responses comprises assessing signalstrengths of the responses.
 7. The external device of claim 1, furthercomprising switching circuitry, wherein the switching circuitry isbetween the transceiver circuitry and each of the plurality of coils. 8.The external device of claim 7, wherein the switching circuitry iscontrolled by the controller circuitry to couple only one of the coilsto the transceiver circuitry at one time.
 9. The external device ofclaim 1, wherein the transceiver circuitry comprises a plurality oftransceiver circuits each coupled to one of the plurality of coils. 10.The external device of claim 9, further comprising switching circuitry,wherein the switching circuitry is between the controller circuitry andeach of the transceiver circuits.
 11. The external device of claim 10,wherein the switching circuitry is controlled by the controllercircuitry to couple only one of the transceiver circuits to thecontroller circuitry at one time.
 12. An external device forcommunicating with or providing power to an implantable medical device,comprising: a plurality of coils each wound around an axis, wherein noneof the axes are parallel to each other; transceiver circuitry coupled tothe plurality of coils; and controller circuitry for controlling thetransceiver circuitry by executing an algorithm, the algorithmcomprising: (a) transmitting a test signal from a first of the pluralityof coils; (b) receiving at the first coil a response to the test signalfrom the implantable medical device; (c) assessing the response at thecontroller circuitry; (d) if the response at the first coil issatisfactory, activating the first coil to telemeter data or power to bereceived by at least one device coil in the implantable medical device;(e) if the response at the first coil is not satisfactory, repeatingsteps (a)-(c) for a second of the plurality of coils; and (f) if theresponse at the second coil is satisfactory, activating the second coilto telemeter data or power to be received by at least one device coil inthe implantable medical device.
 13. The method of claim 12, wherein thealgorithm further comprises: (g) if the response at the second coil isnot satisfactory, repeating steps (a)-(c) for a third of the pluralityof coils; and (f) if the response at the third coil is satisfactory,activating the third coil to telemeter data or power to be received byat least one device coil in the implantable medical device.
 14. Theexternal device of claim 12, wherein the external device is sized to fita user's hand.
 15. The external device of claim 12, wherein thecontroller circuitry comprises a microcontroller.
 16. The externaldevice of claim 12, wherein the plurality of coils are wound around axesthat are orthogonal to each other.
 17. The external device of claim 12,wherein assessing the response comprises assessing a signal strength ofthe response.
 18. The external device of claim 12, further comprisingswitching circuitry, wherein the switching circuitry is between thetransceiver circuitry and each of the plurality of coils.
 19. Theexternal device of claim 18, wherein the switching circuitry iscontrolled by the controller circuitry to couple only one of the coilsto the transceiver circuitry at one time.
 20. The external device ofclaim 12, wherein the transceiver circuitry comprises a plurality oftransceiver circuits each coupled to one of the plurality of coils. 21.The external device of claim 20, further comprising switching circuitry,wherein the switching circuitry is between the controller circuitry andeach of the transceiver circuits.
 22. The external device of claim 21,wherein the switching circuitry is controlled by the controllercircuitry to couple only one of the transceiver circuits to thecontroller circuitry at one time.
 23. The external device of claim 12,further comprising a memory accessible by the controller circuitry. 24.The external device of claim 12, wherein the memory stores historicaldata regarding which of the plurality of coils have been activated bythe algorithm, and wherein the first coil is chosen using the historicaldata.
 25. The external device of claim 24, wherein the second coil isalso chosen using the historical data.